Enhanced plasmonic nanoparticles for cancer therapy and diagnostics

ABSTRACT

One or more techniques and/or products are disclosed using a process for preparing metallic nanoparticles. Resulting nanoparticles may comprise a gold-silver-gold core-shell-shell nanoparticles. Such nanoparticles can be formed by forming a gold core, providing certain materials to form a silver shell, and providing certain materials to form a gold shell. The metallic nanoparticles may be used in molecular sensing, catalysis, photothermal therapy, and other biologically-relevant technologies.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 15/060,180 filed on Mar. 3, 2016, and titled ENHANCED PLASMONICNANOPARTICLES FOR CANCER THERAPY AND DIAGNOSTICS, which claims priorityto provisional patent application, U.S. Ser. No. 62/127,325, entitledENHANCED PLASMONIC NANOPARTICLES FOR CANCER THERAPY AND DIAGNOSTICS,filed Mar. 3, 2015, which is incorporated herein by reference.

BACKGROUND

Metallic nanoparticles composed of gold and silver may possess desiredchemical, electronic, and optical properties, including an ability forsize-controlled synthesis, stabilization, functionalization, andbio-compatibility. Due to these properties, metallic nanoparticles mayallow for desired applications in the fields of molecular sensing,catalysis, photothermal therapy, and biologically-relevant technologies,such as bio-imaging and bio-sensing. For example, photothermal therapymay provide a non-invasive approach that can have fewer side effectsthan conventional treatment, such as chemotherapy and/or radiationtherapy. A variety of plasmonic metallic nanoparticles may havepotential use in photothermal therapy, including gold nanorods, silvernanorods, gold nanocages, silica-gold core-shell, and gold nanoparticlescoated with reduced graphene oxide. Photothermal therapy may utilizeplasmonic nanoparticles with near-infrared wavelength absorption in theranging from about 800 nm to about 1300 nm. Due to the plasmonicenhancement of the metallic portions of the nanoparticle, thesenanoparticles can absorb light in the near-infrared wavelengths,corresponding to the optical window in biological tissues. Thenanoparticles can convert the absorbed light into heat through anonradiative process leading to a localized photothermal effect that canbe used for photothermal therapy, and/or non-invasive bio-imaging due totheir tunable optical properties and their biocompatibility.

Metallic nanoparticles may be difficult to synthesize and keep stable incolloidal suspensions, and some inherent properties of the metals orother materials used in the nanoparticles may present limitations. As anexample, spherical gold nanoparticles may possess a very low lightabsorbance at near-infrared wavelengths, so they may not be preferredfor potential biological applications, such as photothermal therapy anddiagnostics. In another example, the thickness of the nanoparticle,which can affect its properties and potential applications, may bedifficult to control in processing. In yet another example, if ananoparticle comprises a non-metallic portion, such as gold-coatedsilica nanoparticles, the resulting particle may have a smallerplasmonic enhancement property than metallic nanoparticles, due to theirnon-metallic core. Although silica-based plasmonic nanoparticles mayhave desirable light absorbance at near-infrared wavelengths, theirnon-fully metallic composition can reduce their conversion of light toheat efficiency, which can make them less effective in killing cancercells. In another example, both gold-reduced graphene oxidenanoparticles and gold nanorods may absorb at the near-infraredwavelength window. However, synthesis of a uniform reduced grapheneoxide shell can be difficult, reproducibility of the gold nanorods maybe difficult, and the gold nanorods can be unstable over long period oftimes.

SUMMARY

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key factors oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter.

In one implementation, one or more techniques and/or products aredisclosed for preparing metallic nanoparticles comprising: 1) adding afirst citrate compound to a gold solution resulting in a gold coresolution comprising at least one gold core; 2) adding ascorbic acid, asilver compound, and a strong base to the gold core solution resultingin a silver shell on at least one gold core; and 3) adding a secondcitrate compound, hydroquinone, and gold compound to at least one silvershell on at least one gold core resulting in an outer gold shell on thesilver shell.

To the accomplishment of the foregoing and related ends, the followingdescription and annexed drawings set forth certain illustrative aspectsand implementations. These are indicative of but a few of the variousways in which one or more aspects may be employed. Other aspects,advantages and novel features of the disclosure will become apparentfrom the following detailed description when considered in conjunctionwith the annexed drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

What is disclosed herein may take physical form in certain parts andarrangement of parts, and will be described in detail in thisspecification and illustrated in the accompanying drawings which form apart hereof and wherein:

FIG. 1 is a flow diagram illustrating a process for the synthesis ofnanoparticles, which is disclosed herein.

FIG. 2 illustrates characteristics of the nanoparticles prepared by theprocess described.

FIG. 3 illustrates characteristics of the nanoparticles prepared by theprocess described.

FIG. 4 illustrates characteristics of the nanoparticles prepared by theprocess described.

FIG. 5 illustrates characteristics of the nanoparticles prepared by theprocess described.

FIG. 6 illustrates characteristics of the nanoparticles prepared by theprocess described.

FIG. 7 illustrates characteristics of the nanoparticles prepared by theprocess described.

FIG. 8 illustrates characteristics of the nanoparticles prepared by theprocess described.

FIG. 9 illustrates characteristics of the nanoparticles prepared by theprocess described.

FIG. 10 illustrates characteristics of the nanoparticles prepared by theprocess described.

DETAILED DESCRIPTION

The claimed subject matter is now described with reference to thedrawings, wherein like reference numerals are generally used to refer tolike elements throughout. In the following description, for purposes ofexplanation, numerous specific details are set forth in order to providea thorough understanding of the claimed subject matter. It may beevident, however, that the claimed subject matter may be practicedwithout these specific details. In other instances, structures anddevices are shown in block diagram form in order to facilitatedescribing the claimed subject matter. FIG. 1 provides a process forpreparing nanoparticles that may provide the plasmonic enhancement ofboth gold and silver nanoparticles. Nanoparticles may be particles thatrange in size from about 1 nm to about 100 nm. Nanoparticles may also bedifferent shapes, including but not limited to, spheres, rods, cubes,and discs. The process illustrated in FIG. 1 is a method of makinggold-silver-gold core-shell-shell nanoparticles. The metallicnanoparticles may provide plasmon-enhanced absorption in thenear-infrared (NIR) photon energies and may offer opportunities forbiologically relevant applications. In one implementation, the metallicnanoparticles prepared by the process illustrated in FIG. 1 may be usedfor biologically relevant applications including photothermal cancertherapy and biosensing for applications in biolabeling, drug delivery,non-invasive bioimaging, and photothermal therapy.

In certain applications, the nanoparticles may absorb light in the NIRwavelengths and convert it to heat through non-radiative processes,which may lead to a localized photothermal effect. In oneimplementation, the gold-silver-gold core-shell-shell nanoparticle, asshown in FIG. 1, may allow for improved localized heating effects, whichmay result from the gold and silver composition, when compared toalternate nanomaterials. In the process illustrated in FIG. 1, the NIRphotothermal efficiency may be altered, either increasing or decreasing,in order to provide certain desired biologically relevant applications.In one implementation, the thicknesses of the gold core, silver shell,and gold shell may alter the NIR photothermal efficiency. In anotherimplementation, the ratio of the outer gold shell thickness to theoverall particle size may show a linear dependence with the position ofthe plasmon extinction peak wavelength and may alter the NIRphotothermal efficiency. Further, the gold-silver-gold core-shell-shellmetallic nanoparticles illustrated may comprise tunable opticalproperties that have a higher light absorption in the near-infraredwavelength optical window; and the nanoparticles may exhibit plasmonicenhancement and controllable extinction spectra extending from theultraviolet (UV) to the near-infrared absorption wavelengths. In thisexample implementation, FIG. 1 illustrates a series of steps in which agold core 102 is provided. A silver shell 104 is formed around the goldcore 102. Additionally, an outer gold shell 106 is formed around thesilver shell 104.

In one implementation of FIG. 1, techniques are disclosed for a processof preparing nanoparticles comprising: 1) adding citrate compound to agold solution resulting in a gold core solution comprising at least onegold core 102; 2) adding ascorbic acid, a silver compound, and a strongbase to the gold core solution resulting in a silver shell 104 on atleast one gold core 102; and 3) adding a second citrate compound,hydroquinone, and a gold compound to at least one silver shell 104 on atleast one gold core 102 resulting in an outer gold shell 106 on thesilver shell 104.

In another implementation of the process provided in FIG. 1, twelvenanometer (12 nm) gold nanoparticles may be prepared by reducingAu³⁺(HAuCl_(4(aq))) to Au⁰ using sodium citrate in water under boilingconditions to form a gold core 102. Further, a silver shell 104 may beformed around the gold core 102 by reducing Ag²⁺ to Ag⁰ using L-ascorbicacid under basic aqueous conditions at room temperature. The forming ofa silver shell 104 may be iterated at least until an appropriate desiredthickness of the silver shell 104 is obtained. Additionally, an outergold shell 106 may be formed around the silver shell 104 (e.g., orrespective silver shells) by reducing Au³⁺ to Au⁰ using sodium citrateand hydroquinone in water at room temperature. The thickness of theouter gold shell 106 may be controlled by varying the concentrations ofAu³⁺ and hydroquinone in solution.

In FIG. 1, the first citrate compound may be added to a gold solution.In one implementation, the first citrate compound may be sodium citrate.In another implementation, the first citrate compound may be a salt withthe citrate ion. In another implementation, the first citrate compoundmay be potassium citrate. In yet another implementation, the firstcitrate compound may be citric acid. In this implementation, the firstcitrate compound may be added to the gold solution, resulting in thereduction of gold, facilitated by the citrate ion of the first citratecompound. In one implementation, the first citrate compound may coat thegold in the gold solution and act as a capping agent. In anotherimplementation, the first citrate compound may act to control the sizeof the gold core 102. In another implementation, the first citratecompound may act as a capping agent and contribute to the size of thegold core 102.

In FIG. 1, one implementation of an example process may include the useof a gold solution comprising a gold compound and a liquid. In oneimplementation, the liquid may be tap water, distilled water, ordeionized water. For FIG. 1, yet another implementation of an exampleprocess may include using a liquid comprising ultrapure water. Ultrapurewater may be water that has been treated in an ultrapurificationprocess. The ultrapurification process provides highly pure water thatcan limit the salts in the water. Ultrapure water may also have reducedamounts of contaminants, including but not limited to organic andinorganic compounds, dissolved and particulate matter, volatiles andnon-volatiles, reactive and inert substances, hydrophilic andhydrophobic substances, and dissolved gases. The pH and resistivity maybe measured for the ultrapure water in order to check its quality.

In one implementation, the gold solution may comprise about 0.05% toabout 5% gold chloride by weight. In another implementation, the goldsolution may comprise about 95% to about 99.5% ultrapure water byweight. In one implementation, the gold solution may comprise goldchloride as the gold compound. Gold chloride, HAuCl₄ or AuCl₄—, mayinclude Gold(I) chloride, Gold(III) chloride, Gold(I,III) chloride, or acombination of these chemicals. In another implementation, the goldsolution may comprise chloroauric acid, HAuCl₄. During the processdescribed, the formation of the gold core solution comprising the firstcitrate compound and the gold solution result in the formation at leastone gold core.

In order to provide the silver shell around the gold core, a silversolution may be used. In one implementation, the silver solution maycomprise ascorbic acid, a silver compound, and a strong base. In anotherimplementation, the silver compound may comprise silver nitrate. In yetanother implementation, the silver compound may comprise silver and anon-reactive portion of that silver compound. During the processdescribed, a strong base may be used to adjust the pH to basic. In oneimplementation, the strong base may comprise sodium hydroxide. Inanother implementation, potassium hydroxide may be used as the strongbase. During the process described, the silver solution comprisingascorbic acid, the silver compound, and the strong base react to form atleast one silver shell.

After at least one silver shell has been added to the gold core, atleast one particle may be separated from the gold core solution anddispersed in a liquid. In one implementation, the liquid may be may betap water, distilled water, or deionized water. In anotherimplementation, the liquid may be ultrapure water.

After at least one particle is dispersed in the liquid, a second citratecompound, hydroquinone, and a gold compound may be added to form anouter gold shell on top of the silver shell. In one implementation, thesecond citrate compound may comprise sodium citrate. In yet anotherimplementation, the gold compound may comprise gold chloride.

The near-infrared wavelength absorption in the optical window exhibitedby the example gold-silver-gold core-shell-shell nanoparticle of FIG. 1,ranging from about 800 nm to about 1300 nm, may provide a range wherelight can penetrate to a desired depth in biological tissues forphotothermal therapy and non-invasive bio-imaging, resulting in alocalized optical enhancement and photothermal effect when treatingthese biological tissues.

In one implementation, the gold-silver-gold core-shell-shellnanoparticles can be size-dependent and show significantly enhancedplasmonic properties. In another implementation for the nanoparticle,the ratio of the outer gold shell thickness to the overall particle sizemay provide a linear dependence with the position of the plasmonextinction peak wavelength. Temperature measurements after laserirradiation may show that the colloidal gold-silver-goldcore-shell-shell nanoparticles have a higher photothermal effectcompared to spherical gold nanoparticles and gold nanorods. In addition,the outer gold shell surface may allow for biological functionalizationfor cancer targeting and other technologies.

The gold-silver-gold core shell-shell nanoparticle provided by theprocess in FIG. 1 may be spherical or rod-shaped. In one implementation,the size of the core and shells can be tuned to obtain nanoparticleswith diameters ranging from about 10 nm to about 200 nm. The opticalproperties of the nanoparticles are widely tunable and size-dependent.Additionally, the nanoparticles provided in FIG. 1 may be stable as acolloidal suspension in water. In FIG. 1, another implementation of theprocess may provide extended core-shell architectures with speciallydesigned core and shell dimensions with multiple layers of shells. Instill another implementation, the metallic gold-silver-goldcore-shell-shell nanoparticle where the silver shell 104 and outer goldshell 106 can be relatively uniform thicknesses.

For the process shown in FIG. 1, one implementation may include thesilver shell 104 configured to a desired width. In anotherimplementation, additional silver shells and/or gold shells may be addedduring the process of forming the nanoparticles described in FIG. 1. Inone implementation, the process may include at least the gold core 102,a silver shell 104, an outer gold shell 106 where additional silvershells and/or gold shells are added either: 1) between the silver shell104 and outer gold shell 106; and/or 2) to the outer gold shell 106. Inanother implementation, at least two additional silver shells and/orgold shells may be added to the nanoparticle. Additional silver shellsand/or gold shells may be added to provide different qualities to thenanoparticles. Additional silver shells and/or gold shells may also beadded to increase the size or thickness of the nanoparticles. In oneimplementation, ascorbic acid, a silver compound, and a strong base maybe used to form an additional silver shell. For example, an additionallayer of silver may be formed on the silver shell 104 in order toincrease the width of the silver shell 104 layer. In another example,the additional layer of silver may be formed by adding ascorbic acid,silver nitrate, and sodium hydroxide. In one implementation, anotherlayer of silver may be introduced onto the silver shell 104 by addingascorbic acid, silver nitrate, and sodium hydroxide. This additionallayer of silver may be added while the particles are within the goldcore solution or in another liquid. In one example, the liquid may beultrapure water.

In FIG. 1, another implementation may include the outer gold shell 106configured to a desired width. In one implementation, a second citratecompound, hydroquinone, and a gold compound may be used to form anadditional gold shell. For example, an additional layer of gold may beformed on the outer gold shell 106 by the addition of the sodiumcitrate, hydroquinone, and gold chloride. The sodium citrate,hydroquinone, and gold chloride react to form the outer gold shell. Theadditional gold may be added to the outer gold shell 106 on the silvershell 104 or on top of any additional silver added to the silver shell104. In one implementation, another layer of gold may be introduced ontothe outer gold shell.

FIG. 2 provides several implementations of the core-shell-shellnanoparticles through high-resolution transmission electron microscopy(HR-TEM) with various core-shell-shell particle sizes. The HR-TEM, inaddition to extinction spectroscopy and photothermal measurements, maybe used to characterize the nanoparticles. The HR-TEM images ofgold-silver-gold core-shell-shell nanoparticles provided in FIG. 2provide an illustration of the nanoparticles with diameters of (a)12-12-12 nm, (b) 12-18-10 nm, (c) 12-24-10 nm, (d) 12-12-5 nm, (e)12-18-10 nm, and (f) 12-24-10 nm core-shell-shell sizes, respectively.The images provided in FIG. 2 (a)-(f) show selected HR-TEM images of thegold-silver-gold core-shell-shell nanoparticles with a 12±0.9 nm goldcore and various silver and gold shell thicknesses. After the additionof the silver shell, the surface plasmon resonance peak may blueshiftfrom 513 nm for the gold core to approximately 420 nm for thegold-silver core-shell nanoparticles. The plasmon extinction peak maythen broaden, and may increase in intensity as the thickness of thesilver shell is increased.

For the core-shell-shell nanoparticles such as those provided in FIG. 2,localized surface plasmon resonances, characterized by the coherentoscillations of free electrons under incident light, at thenanoparticles surface may be dependent on the nanoparticle composition,size, shape and surrounding medium. In one implementation, the plasmonresonances may lead to certain optical field enhancements. The plasmonextinction peak wavelength of the gold-silver-gold core-shell-shellnanoparticles may also depend on the ratio of the thickness of the outergold shell to the overall size of the nanoparticle. In oneimplementation, the surface plasmon resonance peaks of thesenanostructures can also be tuned from the visible to the near infraredwavelength region by controlling the dimensions of the core and theshells.

FIG. 3 may provide an example of the extinction spectra of the colloidalgold-silver-gold core-shell-shell nanoparticles with a 12±0.9 nm goldcore and various silver and gold shell thicknesses. After the formationof the outer gold shell 106, the plasmon peak generally redshiftsleading to enhanced extinction in the near-infrared wavelength region.FIG. 3(a) may illustrate the normalized extinction spectra ofgold-silver-gold core-shell-shell nanoparticles with a 12±0.9 nm goldcore 102, a 12±1.1 nm silver shell 104, and an outer gold shell 106 ofthickness 5±0.6 nm, 15±0.9 nm, 20±1.6 nm, and 30±2.4 nm, respectively.For the thinnest gold shell of about 5 nm, the plasmon peak may becentered near about 565 nm and extends to the near-infrared wavelengthregion. As the thickness of the outer gold shell 106 may be increased,the plasmon peak may broaden and its maximum may progressively redshiftto the near-infrared wavelength region. At an outer gold shell thicknessof 30±2.4 nm, the plasmon peak may be centered near about 850 nm.

FIG. 3(b) may provide an additional example of the effect of varying thethickness of the silver shell 104. In one implementation, FIG. 3(b) mayillustrate the extinction spectra of gold-silver-gold core-shell-shellnanoparticles with a 12±0.9 nm gold core, a 18±1.6 nm silver shell, andan outer gold shell thickness of 5±0.6 nm, 7.5±0.8 nm, and 10±1.1 nm,respectively. Similar to FIG. 3(a), the gold-shell-shell nanoparticleswith the thinnest gold shell of about 5 nm may have a plasmon peakcentered near about 565 nm that extends to the near-infrared wavelengthregion. In another implementation, increasing the thickness of the outergold shell to a diameter of about 10 nm may redshift the plasmon peakwavelength to about 585 nm.

FIG. 3(c) may provide an example of the extinction spectra of thegold-silver-gold core-shell-shell nanoparticles with a 12±0.9 nm goldcore, a 24±2.1 nm silver shell, and an outer gold shell thickness of5±0.7 nm, 7.5±0.9 nm, and 10±1.1 nm, respectively. In one implementationfor the thinnest gold shell of about 5 nm diameter, the plasmon peak maybe centered at about 610 nm and may extend to the near-infraredwavelength region. In another implementation as the thickness of thegold shell may be increased, the plasmon peak may first blueshift, thenan additional peak centered in the NIR may rise and increase inintensity. The plasmon-enhanced extinction spectra can be controlledfrom the UV to the NIR wavelengths by varying the silver and gold shellsizes, providing many biologically-relevant applications such asphotothermal therapy and bioimaging.

As shown in FIG. 3(d), the plasmon extinction peak wavelength may varywith the ratio of thickness of the outer gold shell to the overall sizeof the nanoparticle. In the example for FIG. 3(d), the equation of thebest fit line may be given by a slope of 1.44×10⁻³±2.9×10⁻⁵ nm⁻¹ and ay-intercept of −0.64±0.02. In this example, varying the ratio ofthickness of the outer gold shell to the overall size of thenanoparticle may provide a mechanism to control the plasmonic opticalproperties of the colloidal gold-silver-gold core-shell-shellnanoparticles with respect to the application.

FIG. 4 provides a photothermal study of different nanoparticle samples.In this example, the temperature of the 54 nm colloidal gold-silver-goldcore-shell-shell nanoparticle sample with a 12 nm core, a 12 nm silvershell, and a 20 nm outer gold shell as a function of time afterirradiation with 800 nm laser light may be compared to correspondingmeasurements on colloidal gold nanorods with about a 10 nm width andabout a 35 nm length in water, 54 nm spherical colloidal goldnanoparticles in water, and an ultrapure water control sample. The waterand spherical colloidal gold nanoparticle samples may not exhibit anydetectable temperature change after laser irradiation. In this example,the colloidal core-shell-shell nanoparticles show a temperature changeof about 5.2±0.2° C. at a rate of about 1.5° C. per minute due to theconversion of the absorbed NIR light to heat by the plasmonicnanoparticles, and the gold nanorods show a temperature change of about3.7±0.2° C. at a rate of about 0.75° C./min.

FIG. 5 provides an example of a normalized extinction spectra of 12 nmcolloidal gold nanoparticles, 30 nm colloidal gold-silver core-shellnanoparticles, 35 nm colloidal gold-silver-gold core-shell-shellnanoparticles, 47 nm colloidal gold-silver-gold-silvercore-shell-shell-shell nanoparticles, and 53 nm colloidalgold-silver-gold-silver-gold core-shell-shell-shell-shell nanoparticles,respectively. In this example, the plasmon extinction peak wavelengthmay correlate with the composition of the outer gold shell 106 of thenanoparticle. For example, when the outer shell composition is gold, theplasmon extinction peak wavelength ranges from about 550 to about 600nm. However, if the outer shell is silver, the plasmon extinction peakwavelength ranges from about 400 to about 450 nm. In addition, everysequential shell of alternating gold or silver composition may broadenthe plasmon extinction peak while redshifting it further to the NIRwavelengths. Further, the extinction peak wavelength of the extendedgold-silver-gold-silver-gold nanoparticles with multiple alternatinggold and silver shells may not follow trends shown in FIG. 3(d).

FIG. 6 provides additional examples of the extinction spectra of (e) 12nm gold nanoparticles and (f) 24 nm, 30 nm, and 36 nm gold-silvercore-shell nanoparticles. The extinction spectrum of the 12 nm colloidalgold nanoparticles may be fit for the light scattering of particlesusing Mie theory at a concentration is 2.9×1011 nanoparticles permilliliter.

FIG. 7 provides additional examples of HR-TEM images of thegold-silver-gold core-shell-shell nanoparticle samples with differentoverall diameters of about (a) 29 nm, (b) 39 nm, (c) 44 nm, (d) 54 nm,(e) 35 nm, (f) 37.5 nm, (g) 40 nm, (h) 41 nm, (i) 44 nm, (j) 46 nm,respectively, and (k) gold nanorods of 10 nm width and 35 nm length.

Similarly, FIG. 8 provides additional examples of HR-TEM images of the53 nm gold-silver-gold-silver-gold core-shell-shell-shell-shellnanoparticles.

FIG. 9 shows a schematic diagram of the example experimental setup thatmay be used for a photothermal study. Within the diagram, an oscillatorlaser 902 may be transmitted through a solution comprising thecore-shell-shell nanoparticles 906 where a thermocouple 904 and acomputer 910 may be used for recording temperatures during theexperimentation. In one implementation, the oscillator laser 902 madefrom titanium-sapphire may have an average power of about 2.6 W and 70fs pulses centered at 800 nm with a repetition rate of 80 MHz andattenuated to 1.2 W. In another implementation, the oscillator laser 902made from titanium-sapphire produces 0.7 mJ, 75 fs pulses centered at800 nm with a repetition rate of 10 kHz. A beam block 908 can act as anoptical filter and may absorb the 800 nm laser 902 provided for theexperimentation.

FIG. 10 provides yet another example of the extinction spectra of the 54nm spherical colloidal gold nanoparticles, the colloidal gold nanorods(about 10 nm width and about 35 nm length) at a concentration of about3.0×10¹ nanoparticles per milliliter, and the 54 nm colloidalgold-silver-gold core-shell-shell nanoparticles (sample CSS4) used inthe photothermal study. The extinction of the spherical goldnanoparticles may be overlapped with the best fit using Mie theory(dotted black line) at a concentration of about 2.8×10¹⁰ nanoparticlesper milliliter.

Additionally, a functionalized group may be added to thegold-silver-gold core-shell-shell nanoparticles. The gold-silver-goldcore-shell-shell nanoparticles can be thiolated and functionalized forpotential biochemical applications and sensing applications. In oneimplementation, a functionalized group may be added when molecules withan exposed thiol may attach to the outer gold shell of the nanoparticlesurface, forming a relatively strong gold-thiol bond. In anotherimplementation, a range of molecular and biomolecular functionalizationmay be attached to the nanoparticle surface to improve biologicalstability and selectivity, depending on the desired application. In yetanother implementation, functionalizations may include one or more ofthe following: mercaptosuccinic acid, polyethylene glycol, proteins,antibodies, antigens, micro RNA, pharmaceuticals, and fluorescent labelsfor improving biocompatibility, selective binding to biological targets,drug delivery, and/or molecular sensing applications.

Plasmonic gold and silver nanoparticles can be functionalized withbiological molecules, polymers, and/or other groups through thiolationfor applications in several applications, including biolabeling, drugdelivery, and photothermal therapy. In one implementation, the outergold shell may provide a surface for attaching biological molecules,such as proteins and DNA, for cell targeting and drug delivery.

Example 1

For the nanoparticle synthesis, all chemicals may be obtained from asingle supplier, such as Sigma Aldrich, and used without furtherpurification in ultrapure water. For the synthesis of 12 nm goldnanoparticle seeds for the gold core, 30 mL of 290 μM gold chloride inwater is brought to reflux under vigorous stirring conditions, followedby the addition of 900 μL of 34 mM sodium citrate. The colloidalsolution undergoes a color change from pale yellow to bright red afterabout 10 to about 20 minutes and is removed from heat and cooled to roomtemperature. For the growth of the first silver shell, 300 μL of thegold seeds are added to 10 mL ultrapure water. The mixture is kept atroom temperature under vigorous stirring with additions of 60 μL of 100mM ascorbic acid, 15 μL of 100 mM silver nitrate, and 75 μL of 100 mMsodium hydroxide. Ascorbic acid is a mild reducing agent that reducesAg+ onto the gold core under basic conditions. The size of the silvershell can be controlled by selecting the number of ascorbic acid, silvernitrate, and sodium hydroxide sequential additions. The gold-silvercore-shell colloidal nanoparticles are centrifuged at 2,400 rpm for 20minutes and redispersed in 10 mL of ultrapure water. Different sizes ofouter gold shells are then grown by adding 100 μL, 200 μL, or 300 μL of29 mM gold chloride, followed by the addition of 25 μL of 34 mM sodiumcitrate and 100 μL of 0.03 M hydroquinone under vigorous stirring atroom temperature for 60 minutes. These gold-silver-gold core-shell-shellnanoparticles can be easily thiolated and functionalized for potentialbiochemical applications. The three steps involved in the synthesis arerepresented in Scheme 1. Spherical gold nanoparticles and gold nanorodsare used for comparison studies of the photothermal effects of thecolloidal core-shell-shell nanoparticles. Spherical gold nanoparticlesof diameter 54±6 nm are synthesized using a seeding growth techniquereported previously. Here, 250 μL of the 12 nm seed solution, 100 μL of0.03 M hydroquinone, and 22 μL of 34 mM sodium citrate are addedconsecutively to 10.0 mL of 2.9 mM gold chloride solution. The solutionis left at room temperature and under vigorous stirring conditions for60 minutes. The gold nanorod sample is obtained from a supplier, such asNanopartz, has a 10 nm width, a 35 nm length, and is capped withcetyltrimethylammonium bromide in aqueous colloidal suspension.

Example 2

The photothermal performance of 54 nm colloidal gold-silver-goldcore-shell-shell nanoparticles with a 12 nm gold core, a 12 nm silvershell, and a 30 nm outer gold shell are studied in solution under NIRlight. A 0.8 mL volume of the colloidal sample is placed in a 1.0 mmpath-length quartz cuvette and irradiated with a laser beam centered at800 nm with an average power of 1.7 W, a beam size of 1.2±0.2 mm, apulse width of 75 femtosecond (abbreviated as fs), and a repetition rateof 80 MHz. The temperature change is measured using a K typethermocouple connected to a computer using a data acquisition card. Theresults are compared to an ultrapure water sample, the 54±6 nm sphericalcolloidal gold nanoparticle sample at a concentration of 2.8×10¹⁰nanoparticles/mL in water, and the gold nanorods sample at aconcentration of 3.0×10¹¹ nanoparticles/mL. The optical density(OD=0.26) of the plasmon peak of the 54 nm spherical colloidal goldnanoparticles at 540 nm is equal to the optical density of the plasmonpeak of the gold-silver-gold core-shell-shell nanoparticle sample at 800nm as well as the gold nanorod sample at 800 nm for a quantitativecomparison of the photothermal effects of the different nanoparticlesamples. The word “exemplary” is used herein to mean serving as anexample, instance or illustration. Any aspect or design described hereinas “exemplary” is not necessarily to be construed as advantageous overother aspects or designs. Rather, use of the word exemplary is intendedto present concepts in a concrete fashion. As used in this application,the term “or” is intended to mean an inclusive “or” rather than anexclusive “or.” That is, unless specified otherwise, or clear fromcontext, “X employs A or B” is intended to mean any of the naturalinclusive permutations. That is, if X employs A; X employs B; or Xemploys both A and B, then “X employs A or B” is satisfied under any ofthe foregoing instances. Further, at least one of A and B and/or thelike generally means A or B or both A and B. In addition, the articles“a” and “an” as used in this application and the appended claims maygenerally be construed to mean “one or more” unless specified otherwiseor clear from context to be directed to a singular form.

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asexample forms of implementing the claims. Of course, those skilled inthe art will recognize many modifications may be made to thisconfiguration without departing from the scope or spirit of the claimedsubject matter.

Also, although the disclosure has been shown and described with respectto one or more implementations, equivalent alterations and modificationswill occur to others skilled in the art based upon a reading andunderstanding of this specification and the annexed drawings. Thedisclosure includes all such modifications and alterations and islimited only by the scope of the following claims. In particular regardto the various functions performed by the above described components(e.g., elements, resources, etc.), the terms used to describe suchcomponents are intended to correspond, unless otherwise indicated, toany component which performs the specified function of the describedcomponent (e.g., that is functionally equivalent), even though notstructurally equivalent to the disclosed structure which performs thefunction in the herein illustrated exemplary implementations of thedisclosure.

In addition, while a particular feature of the disclosure may have beendisclosed with respect to only one of several implementations, suchfeature may be combined with one or more other features of the otherimplementations as may be desired and advantageous for any given orparticular application. Furthermore, to the extent that the terms“includes,” “having,” “has,” “with,” or variants thereof are used ineither the detailed description or the claims, such terms are intendedto be inclusive in a manner similar to the term “comprising.”

The implementations have been described, hereinabove. It will beapparent to those skilled in the art that the above methods andapparatuses may incorporate changes and modifications without departingfrom the general scope of this invention. It is intended to include allsuch modifications and alterations in so far as they come within thescope of the appended claims or the equivalents thereof.

What is claimed is:
 1. A process of preparing metallic nanoparticlescomprising: adding a first citrate compound to a gold solution resultingin a gold core solution comprising at least one gold core; addingascorbic acid, a silver compound, and a strong base to the gold coresolution resulting in a silver shell on at least one gold core; andadding a second citrate compound, hydroquinone, and a gold compound toat least one silver shell on at least one gold core resulting in anouter gold shell on the silver shell.
 2. The process of claim 1, whereinthe first citrate compound and second citrate compound respectivelycomprise sodium citrate.
 3. The process of claim 1, wherein the goldsolution comprises gold chloride and ultrapure water.
 4. The process ofclaim 1, wherein the silver compound comprises silver nitrate.
 5. Theprocess of claim 1, wherein the strong base comprises sodium hydroxide.6. The process of claim 1, wherein the silver shell and outer gold shellare uniform thicknesses.
 7. The process of claim 1, the silver shellconfigured to a desired width.
 8. The process of claim 7 furthercomprising the step of increasing the thickness of the silver shell tothe desired width by adding ascorbic acid, the silver compound, and thestrong base.
 9. The process of claim 1, the outer gold shell configuredto a desired width.
 10. The process of claim 1 further comprising thesteps of: thiolating the nanoparticles; and functionalizing thenanoparticles.
 11. The process of claim 1 further comprising the step ofadding at least one additional gold shell to the outer gold shell of themetallic nanoparticles.
 12. The process of claim 1 further comprisingthe step of adding at least one additional silver shell to the outergold shell of the metallic nanoparticles.